The present invention relates in general to part/material replenishment for product manufacture and/or assembly systems and the like, and is particularly directed the use of an elapsed time clock in conjunction with the call tag employed in the wireless call tag-based material replenishment system described in the above-referenced co-pending Bacon et al application. The elapsed time clock serves essentially as a call tag xe2x80x98stop watchxe2x80x99, that is reset whenever a part replenishment call is made, and thereby functions to inform workstation personnel of the length of time that has elapsed since the last part call from that tag.
As described in the above-referenced co-pending application, product manufacturers widely employ a technique, referred to as xe2x80x98pull manufacturingxe2x80x99, to replenish components or material required by an assembly line-side workstation in the course of its participation in the production of an item. In accordance with this resupply scheme, parts or material required by a line-side workstation are resupplied in response to a request or xe2x80x98callxe2x80x99 from the workstation to a remote storage management and distribution subsystem, which then retrieves some number of the requested part from a storage facility and delivers them to the requesting site.
Unfortunately, within most manufacturing environments, options for communicating material replenishment requests to those responsible for delivering the parts are considerably limited. A significant number of production facilities continue to employ traditional manual, labor-intensive routines, such as card-based methods. Others, which have attempted to incorporate upgraded communication methods, use hardwired subsystems, that are not only costly to install but, due to their inherent inflexibility, are expensive, time consuming, and labor intensive to retrofit or modify, as the needs and/or retooling of the plant are continually being updated and reconfigured. Although some wireless forms of call systems have been proposed, they are complexxe2x80x94requiring two-way communications with a line-side locationxe2x80x94and are therefore very expensive to install and operate.
Pursuant to the invention described in the above-referenced co-pending application, shortcomings of conventional pull manufacturing replenishment systems are obviated by a wireless xe2x80x98call tagxe2x80x99 based system. In accordance with this call tag based scheme, diagrammatically shown in FIG. 1, advantage of the detection and signal processing infrastructure of the tagged object radio location system described in the U.S. Pat. No. 5,920,287, to D. Belcher et al (hereinafter referred to as the ""287 patent), by installing one or more xe2x80x98call tagsxe2x80x99 16 at or in proximity of each plant workstation 13 of one or more assembly lines 15 within a manufacturing plant 12. If a workstation employs different components, it is equipped with multiple call tagsxe2x80x94one for each different part.
A respective call tag 16 may have a physical configuration, shown in FIG. 2 as including a housing 30, that contains various input/output (I/O) units associated with the use of the call tag, such as a xe2x80x98part callxe2x80x99 push-button 32, and an optical indicator 36. The push-button 32 is employed by a (line-side) operator to trigger the operation (part call transmission) of the call tag. The optical indicator 36 may comprise a light emitting diode (LED), or the like, that is illuminated or flashed when a part replenishment call signal is transmitted by the call tag.
To initiate part replenishment, a line-side workstation operator simply pushes the tag""s xe2x80x98callxe2x80x99 button 32. This causes the call tag""s internal RF transmitter to transmit a spread spectrum RF transmitter to transmit a spread spectrum RF signal burst that is encoded with the identification (e.g., serial number) of the call tag. At the same time, the call tag""s optical indicator 36 (e.g., LED) is flashed to provide a visual indication that the xe2x80x98part callxe2x80x99 was transmitted. The transmitted RF burst is detected by one or more transmission readers 10 of a spatially distributed transmission burst detection and processing subsystem 24. In addition to having the ability to perform tag geolocation processing of the type described in the ""287 patent, the signal processing subsystem 24 reads identification and other data conveyed in each call tag transmission. The call tag identification data is used by a resource management operator to access an asset management database 20, which associates each call tag""s identity with a part employed by the site where the call tag is located. This enables the resource management operator to specify what component is to be accessed from storage, so that the part may be delivered to the identified call tag""s workstation.
Because of the effectively continuously dynamic character of assembly line production, including differences among production shifts and operator assignments, coupled with the ease with which the call tag system described above enables workstation personnel to request material replenishment (simply by pushing a button), system operators may not be particularly diligent in keeping track of replenishment orders. This can lead to duplicate and triplicate orders, as well as out of stock conditions. Moreover, a subsystem failure or an anomaly in the replenishment path, which could lead to assembly line slow down or interruption, may not be immediately noticed. It would be desirable, therefore, to know how recently a parts call has been made. Not only would this advise lineside personnel of the time of the call, but it would aid in determining maximum and minimum inventory levels to be stored lineside.
In accordance with the invention this objective is fulfilled by an enhancement to the call tag-based replenishment system described in the above-referenced copending application, which is effective to continuously inform workstation personnel of the length of time that has elapsed since the last part call was made from a respective call tag. In particular, the present invention includes the incorporation into the call tag of an elapsed time clock, that is automatically reset in response to the call button being pushed, and thereby essentially operates as a part replenishment xe2x80x98stop watchxe2x80x99.
Even though experience of normal assembly line operation will customarily enable a workstation operator to anticipate when to expect parts delivery once a parts call has been made, the incorporation of a part call xe2x80x98stopwatchxe2x80x99 or elapsed time device into the call tag not only allows the lineside operator to determine if an expected delivery is late, but to confirm whether a call was actually made within a given time reference (e.g., an assembly line shift). While the elapsed time clock may be installed and operate as a stand-alone item, it is preferred that it be integrated with other components of the call tag, to facilitate ease of use. In accordance with a non-limiting embodiment of the invention, the call tag timer is arranged to be reset by the operation of the call tag""s pushbutton. As a non-limiting example, the elapsed time may be displayed by way of a dedicated clock display on the call tag housing.